The present invention relates to electrochemical cells and methods for their manufacture. More particularly, the invention relates to double layer capacitors which provide for direct external electrical connection to their electrodes.
Double layer capacitors include at least one inert, high surface-area electrode and an electrolyte. Their capacitance arises from a separation of charged species at the electrolyte-electrode interface (i.e., the xe2x80x9cdouble layerxe2x80x9d); typically the charge separation distance is on the order of atomic dimensions. Particularly, high capacitance double layer capacitors are referred to as xe2x80x9csupercapacitorsxe2x80x9d because of their potentially enormous capacitance (possibly as high as farads or tens of farads per gram). This high capacitance results from a combination of the very small charge separation distance inherent in double layers coupled with a particularly high surface area of the electrodes (often on the order of thousands of meters squared per gram).
A typical double layer capacitor cell contains two electrodes separated by an electrode separator to maintain electrical isolation between the electrodes. These double layer capacitors are charged by applying a voltage across the two electrodes and thereby increasing the total charge stored in the double layer of each electrode. The voltage difference across the two electrodes can continue to increase during charge so long as the leakage current between the electrodes remains low. Ultimately, however, the potential difference between the two electrodes will reach a level where the electrolyte solvent is electrolyzed (introducing a large source of leakage current). Generally, electrolysis of the electrolyte is to be avoided in double layer capacitors because it can cause, among other detrimental effects, loss of electrolyte, increased pressure in the cell, and formation of explosive mixtures (oxygen and hydrogen in the case of aqueous electrolytes).
To attain higher voltages than are feasible in a single double layer capacitor device, multiple double layer capacitors are sometimes connected in series, particularly as xe2x80x9cbipolar stacks.xe2x80x9d Bipolar stacks are generally characterized by a series of cells electrically connected in series through shared electrodes or interconnected electrodes.
Conventional double layer capacitor devices (whether composed of unitary or stacked cells) are typically packaged in a metal container. FIGS. 1A and 1B illustrate simplified examples of such packages.
FIG. 1A shows a conventional capacitor device package of a metal can with protruding leads. The capacitor 100 is composed of a pair of electrodes 102, 104 separated by a separator material 106 and wound into a roll 109. The separator 106 is typically a porous electrically insulting material, such as polyethylene. An electrolyte (not shown) is also present between the two electrodes, typically permeating the separator. The capacitor components are contained in a metal, typically aluminum or steel, can 108. Leads 110 connected to the two electrodes 102, 104 protrude from the can 108 for external electrical connection.
FIG. 1B shows a conventional capacitor device package of a coin cell. The capacitor 120 is again composed of a pair of electrodes 122, 124, in this case disks, separated by a separator material 126. The separator 126 is typically a porous electrically insulting material, such as polyethylene. An electrolyte (not shown) is also present between the two electrodes, typically permeating the separator. The capacitor components are contained in a metal, typically aluminum or steel, package 128 composed of a case 130 and a cap 132. In this package, rather than protruding leads, where the metal package itself acts as a lead for external electrical connection.
Recently, demand has increased for capacitors with surface mount electrical connections, for example, as back-up power sources in electronic devices. While the conventional capacitor designs may be used to meet this need, alternative designs that are easier and less expensive to manufacture would be desirable.
To achieve the foregoing, the present invention provides double layer capacitor cells that provide direct external electrical connection to their electrodes and methods for their manufacture. These cells are lightweight, simple and inexpensive to manufacture, and versatile. They may be used alone or they may be stacked to form bipolar stacked capacitors.
In one aspect, the invention provides an electrochemical capacitor cell. The cell includes a cell container, a pair of electrodes provided within the cell container, a separator provided within the cell container and disposed between the two electrodes, and an electrolyte provided within the cell container. The cell container has a plurality of openings exposing a portion of each of the electrodes for electrical contact.
In another aspect, the invention provides an electrochemical capacitor device. The device a device package and a plurality of stacked electrochemical cells provided within the device package. Each of said cells has a cell container, a pair of electrodes provided within the cell container, a separator provided within the cell container and disposed between the two electrodes, and an electrolyte provided within the cell container. The cell container has a plurality of openings exposing a portion of each of the electrodes for electrical contact.
In other aspects, the invention further provides additional electrochemical capacitor devices. One such device includes a device package and a pair of stacked electrochemical capacitor cells provided within the device package. Each of the cells includes a first electrode with a metal current collector, a second electrode, and a separator disposed between the two electrodes. A cell separator is disposed between the second electrodes of the two cells within the device package, and an electrolyte is provided within the device package. The device package has a plurality of openings exposing a portion of each of the first electrodes of the two cells for electrical contact.
Another such device is an electrochemical capacitor device including a device package having a pair of adjacent cavities and a pair electrochemical capacitor cells, one cell provided within each of the plurality of cavities of the device package. Each of the cells includes a first electrode with a metal current collector, a second electrode, and a separator disposed between the two electrodes. An electrical bridge is disposed between the second electrodes of the two cells within the device package, and an electrolyte is provided within the device package. The device package has a plurality of openings exposing a portion of each of the first electrodes of the two cells for electrical contact.
In another aspect, the invention provides another electrochemical device. This device includes a device package having a non-conductive substrate, vias in the substrate connecting to pads on an exterior surface of the substrate, and a metal lid. The device also includes a plurality of stacked electrochemical cells in accordance with the present invention provided within the device package, and electrodes of the cells are electrically connected to pads by the vias. The electrical connection to one of the exterior pads may be provided by the lid.
In yet another aspect, the invention provide a method of a method of making a stackable electrochemical cell. The method involves forming a cavity in sheet of cell container barrier material, punching a hole through the cell container material in the cavity, loading double layer capacitor components into the cavity over the hole, bonding a second sheet of cell container barrier material having a hole over said capacitor components in the cavity, and sealing said cell.
These and other features and advantages of the present invention are described below with reference to the drawings.